Periodontal bacterial infections induce chronic inflammation which leads to a massive infiltration of acute and chronic inflammatory cells. Interestingly, unlike other chronic inflammatory lesions , only small areas of fibrosis can be seen surrounding the inflammatory lesion. In most areas of infiltration, fibroblasts are non-existent. This loss of fibroblast activity and, therefore, connective tissue leads to diminished integrity of the periodontium. While the fibroblast is the key effector cell in fibrotic areas, its absence from gingival tissue during inflammation is clearly associated with connective tissue loss, and diminished resistance to the damaging effects of inflammation. T lymphocytes are closely associated with early events in periodontal inflammation and may act to stimulate fibroblast activity. The manner in which these cells interact is largely unknown. Our laboratory has discovered that periodontal fibroblasts display CD40, a receptor previously thought to be associated with bone marrow derived cells (e.g. B cells, dendritic cells). The significance of CD40 expression on periodontal fibroblasts is that its ligand (L) is found on T lymphocytes and also on mast cells, and the CD40- CD40L interaction is important for the stimulation of the CD40 expressing cell. The hypothesis to be tested in this proposal is that CD40 is also is also a critical regulatory molecule for fibroblasts, important for their proliferation and synthesis of proinflammatory cytokines and collagen. Disruption of the fibroblast CD40 signaling mechanism may inhibit periodontal inflammation and connective tissue destruction. The importance of periodontal fibroblast CD40 for periodontal inflammation will be determined by answering the following questions: 1) Does CD40 act as a cytokine/growth factor receptor an induce protein tyrosine phosphorylation and fibroblast proliferation? The CD40 signal transduction pathway in periodontal fibroblasts will be examined. Human periodontal fibroblasts will be tested for their ability to proliferate when signaled via CD40. If CD40 acts as a fibroblast growth factor receptor, interference with the signal transduction conduit may blunt fibroblast proliferation and decrease tissue integrity. 2) Does crosslinkage of CD40 induce periodontal fibroblasts to synthesize proinflammatory cytokines and is their collagen production altered? IFN-gamma augments display of CD40 on fibroblasts and crosslinking CD40 induces production of proinflammatory Il-6. Periodontal fibroblasts signaled via CD40 will be studied for induction of other key profibrotic cytokines such as TNF-alpha, TGF-beta, and Il-1. Collagen production by periodontal fibroblasts will be analyzed for modulation due to CD40 signaling. Activation of CD40+ fibroblasts by CD40L+ T cells may be involved in mediating periodontal inflammation and possibly stimulating reparative processes. 3) Does stimulation of the CD40-CD40L system in vitro induce the production of collagenase by gingival fibroblasts? The degradation of periodontal connective tissue during periodontal disease is mediated by matrix metalloproteinases (MMP), such as collagenase, and inhibited by tissue inhibitors of matrix metaalloproteinases (TIMP). Expression of MM{P and TIMP are altered by inflammatory cells and their mediators. Since fibroblasts make MMP and TIMP are altered by inflammatory cells and their mediators. Since fibroblasts make MMP and TIMP, they will be examined for the ability of CD40-CD40L interaction to modulate MMP and TIMP production. Fixed human T cell clones will be used as the source of CD40L. The results of these studies may lead to new concepts of cellular function and interactions in periodontal tissue breakdown and repair.